Process for beneficiating ores



United States Patent PROCESS FOR BENEFICIA'IING ORES John H. Dismant, El Paso, Tex., assignor to International Minerals & Chemical Corporation, a corporation of New York No Drawing. Filed July 21, 1958, Ser. No. 749,584

Claims. (Cl. 209-427) The present invention relates to a processforthe beneficiation of ores. More particularly this invention relates to a process for the recovery of heavy minerals from phosphate ores. Still more particularly, it relates to a process for the recovery of phosphate values and/ or heavy minerals normally discarded in the tailings from the cationic flotation stage of a phosphate flotation process. Specifically, the present invention relates to the recovery of heavy minerals such as ilmentite, rutile and zircon, as Well as certain minerals from ores containing substantial amounts of phosphate rock and siliceous material.

The occurrence of minerals such as ilmenite .(FeTiO zircon (ZrSiO rutile (TiO and monazite ((Ce, La, Y, Th) P0 is widespread. Large deposits occur in the beach sands of Australia, as well as in the beach sands of Florida. Deposits of rutile occur in the Piney River area of Virginia, which deposits contain about 45% by weight of ilmenite. Up to the present time it has been common practice to process or beneficiate only those ores which contain a rather high percentage of such valuable minerals.

Several processes have been developed whereby flotation procedures have been adapted to the recovery of such minerals from their ores. For example, zircon is separated from other constituents such as rutile, ilmenite,

quartz, and monazite when these occur in mineral sands found in certain areas along the beaches in Australia. The sand is preferably washed and reagentized with dilute soap solutions and certain frothing agents or extenders such as pine oil, cresol, or higher alcohols, to form a float. The zircon may be floated away from silica and the other desirable mineral constituents, the zircon-bearing froth separated therefrom, and the other mineral constituents separated from the tailings by subsequent flotation procedures or by suitable gravity methods.

It has been found that in order to achieve a concentration of the desired mineral from ores containing the same by previously used methods, that the concentration of the minerals in the ore must be at least 40% by weight. Furthermore, the operational conditions during flotation procedures must be controlled very carefully in order to produce satisfactory results.

It has recently been discovered that traces of certain metallic minerals, known in the industry as heavy minerals, such as ilmenite, rutile, zircon, sillimanite, as well as minor amounts of garnet, tourmaline, and monazite, occur in association with silica and phophaticrock in the Florida phosphate fields. It is the usual practice in the recovery of the phosphate values from phosphate ores to subject the phosphate ore, which normally has a concentration of heavy minerals of less than 1% by weight, to flotation operations to produce high grade phosphate concentrates. The flotation procedure usually involves a rougher flotation operation utilizing anionic reagents such as fatty acids whereby the phosphate is floated. The phosphate concentrate recovered from the operation is then upgraded to a final concentrate of a grade beteween 72% and .7 8% BPL (bone phosphate of lime) byflotation Patented Aug. 9, .1960

ice

with cationic reagents such as long chain aliphatic amine acid addition salts. The froth or floated product from this amine flotation step is a predominantly silica product containing from about 4% to 20% BPL. In so-called open circuit operation this product, usually called a tailing, is discharged to waste. In a closed circuit type of operation, this product is recirculated; however, it carries so much material as heavy minerals that the closed circuit must periodically be purged and the purged stream sent to Waste.

The composition of the silica concentrates or tailings produced by this method, which heretofore were usually sent to waste, averages about 60 to 70% by weight .of silica and about 4% to 20% by weight of tricalcium phosphate, the remainder consisting of the aforementioned heavy minerals together with other gangue impurities. The heavy mineral concentration averages about 2% to 4% and the present invention is directed to the recovery of these heavy minerals as Well as to the recovery of the phosphate values.

It is an object of the present invention to provide a process for the recovery of metallic minerals from ores containing the same in association with phosphatic and siliceous matter.

It is a further object of the invention to provide a novel process for the recovery of metallic minerals from phosphate ore.

It is a further object of the invention to provide a novel process for the recovery of metallic minerals from phosphatic ores wherein the concentration of the minerals in the ore is less than 1% by weight.

It is another object of this invention to provide a pro cess for the recovery of metallic minerals and phosphate values from a silica tail fraction produced in a phosphate ore flotation process, which heretofore Was lost to waste;

These and other objects of the invention will be obvious to those skilled in the art from the description of the invention.

The total concentration of metallic or heavy minerals in the phosphate matrix which is mined is usually less than 1% by Weight. By subjecting the phosphate rock to. flotation operations for the recovery of the phosphatic values in accordance with well-known and established pro cedures, the metallic mineral content of the tailings of such flotation operations may be increased to 2% to 4% by Weight.

In a typical process for the recovery of phosphate values from Florida pebble phosphate ore, the ore is mined from the natural deposit and transferred to washers and then to flotation plants in which the material is treated in aqueous slurry form. This slurry contains sizable amounts of silica, so-called colloidal phosphates, and clays normally delineated as slimes, as Well as other gangue materials. In the flotation operation the phosphate is recovered in as pure a form as possible and is substantially free of slimes. In a flotation process the phosphate particles must be of such a size that they may be economically treated.

As an initial step in obtaining a flotation slurry, the ore material is subjected to a preliminary Washing operation wherein a sizable quantity of the coarse phosphatic values are removed by a screening operation which produces a pebble product containing all of the +1 mm. values. The 1 mm. values containing the phosphatic particles, silica particles, and the slimes as a slurry must be further processed to give maximum recovery of the granular material and substantially complete removal of the slime material which if allowed to remain would adversely afliect the subsequent concentration process, i.e., silica removal. 7

A rough separation of the slime material may be. ac-

complished in a number of ways. As practiced commercially in the phosphate fields of Florida, recourse is taken to a hydro-separation or hydrocycloue process. The overflow from the hydroseparator or classification system is withdrawn and sent to a settling or slime pond. This overflow is made up chiefly of suspended clay and extremely fine particles of phosphate, i.e., particles of a sufiicient degree of fineness that they could not economically be recovered at any subsequent step of the process. This separation is commoniy made, in the phosphate in dustry, at approximately 150 or 200 mesh. The coarser fraction, essentially l and +150 mesh, is separately withdrawn. Following removal of this fraction, it is sized further; usually by hydraulic classification or screening at about 35 mesh to about 48 mesh. The coarser fraction (i.e., -1 mm. +35 mesh) is then treated for removal of the phosphate values on agglomerate tables, spirals, belts, underwater screens or by froth flotation. The finer fraction (i.e., -35+l50 mesh) is subjected to froth flotation operations.

In the froth flotation operation reagents are employed to selectively float a desired constituent of the ore. If the desired constituent is phosphate, then such reagents as fuel oil, kerosene along with long chain fatty acids and caustic soda, fatty acid soaps and the like are used. In general, the concentrates from rougher flotation steps are subjected to scrubbing with chemical agents to remove flotation reagents and then to secondary flotation operations which float the minor constituents of the concentrates. In the case of phosphate flotation, the reagents utilized in the secondary flotation are amines derived from long chain fatty acids or salts thereof such as the acetate salt. This secondary flotation operation floats the minor constituent of the concentrate, which at this stage of phosphate flotation procedure is silica. Amines and their salts, while effective as flotation reagents for silica, are nevertheless not highly selective, i.e., they are not eifective depressants for phosphates. As a consequence, considerable quantities of phosphate material are floated together with the silica, and this phosphate material is lost in the silica tail which is sent to waste. The silica tail also contains from about 2% to 4% by weight of heavy minerals.

It has now been found that the heavy minerals may be readily recovered from this silica tail fraction when the further described steps of the present invention are followed. While the exact reason is not known, it appears that the cationic fiotation treatment renders the heavy minerals more susceptible to recovery by the described process than has heretofore been noted. In accordance with the present invention, the silica tail fraction is subjected to an electrostatic separation step to produce a heavy mineral concentrate. The silica t-ail fraction is prepared for charging and electrostatic separation by any one or more of a number of preliminary treatments. Ore to be separated electrostatically must be dried to substantially eliminate conductivity of films on the surface of the particles. When the drying is effected by heating the ore, a wide range of temperature may be used, depending upon the degree of separation desired in the electrostatic concentration operation and the nature of the feed. The silica t-ail fraction is heated to dryness at a temperature of at least 150" F. and maintained at a temperature of a least 150 F. up to the point of introduction as free falling bodies into the electrostatic field. Higher temperatures which do not deleteriously affect the mineral can be employed and in many instances are requi-red'in order to satisfactorily prepare the particle surfaces for optimum separations. In general temperatures of between about 200 F. and about 1000 F. produce the desired results. Temperatures Within the range from about 650 F to about 750 F. have produced good results. Obviously the use of temperatures higher than those resulting in optimum beneficiation cannot be justified economically.

Charging of the particles of the silica tail fraction prior to the electrostatic separation through the medium of contact electrification is preferably carried out while particles are at an elevated temperature in the range of approximately 150 F. to approximately 350 P. which requires heating to a temperature in the range of about 150 F. to about 450 F. or higher; however, as previously mentioned, temperatures between 200 F. and about 1000 F. produce the desired results. When heating at a temperature at the lower end of this range, a longer period of time is required to accomplish the desired result of rendering the silica tail fraction susceptible to contact potential methods of charging and likewise at a temperature at the upper end of this range a shorter period of time is required. The time of treatment is generally within the range of from about one minute to about thirty minutes.

Following the heat treatment the silica tail fraction is cooled just prior to its entry into the electrostatic field. The feed material is cooled to a temperature in the range of from about F. to about 450 F. and preferably to a temperature in the range of from about F. to about 200 F. Separation of heat treated ore when substantially cold, however, can be effected.

In order to accomplish electrostatic separation either by the free fall method or by so-called conductivity sepa ration methods, the silica tail particles must be induced to accept an electrical charge. When the separation is made by the free fall method, the ore particles must be differentially electrified before passage through the electrostatic field, i.e., particles of heavy minerals, for example, must carry an electrical charge of different character or of different magnitude from that of the silica.

It has been observed that when a silica tail fraction which still has a cationic reagent thereon is heated and then cooled to a temperature within the ranges hereinbefore set forth, the particles of the silica tail fraction exhibit differential charges and may be directly sent to the electrostatic separator. While it is not definitely known why these particles exhibit dilferential charges, it is believed that the ions of flotation reagents attach themselves at the sites of electrical charges on the particles and probably neutralize these charges. Upon desorption, which occurs whenthe particles are heated, these same reagents should have the effect of charging any particles from which the reagent has been desorbed or removed by heat.

It is, however, generally preferred to charge the particles through the medium of contact electrification. Contact electrification results from the movement of matter in response to such stimuli as differences in escape rate of positive or negative charges, or transfer of electrons or ions across an interface due to differences in energy levels and the like. It has been determined that real crystals never attain the static perfection of an ideal crystal lattice and that a real crystal may have distorted surfaces, displaced ions or atoms, interstitial sites and surface sites, and charge displacement due to separated anion-cation pairs ofabnormal ionized atoms and trapped electrons. It is postulated that these traps are capable of acting as donors and acceptors of electrons and frequently it is these traps that are probably the controlling influences in contact electrification of minerals.

Particles of dissimilar materials, if the surfaces thereof do not exhibit differential electrification upon subjection to contact electrification operations, such as agitation, often can be caused to exhibit differential electrification by thermal, chemical, or electromagnetic methods. The differential charge may be acquired, for example, by rupture of an electrical double layer, by mechanical means, as, for example, from interparticle contact and separation or by transfer of electrons from a source external to the particles or any combination of these methods.

Basically, the desired charging depends on temperature, impurity content, and mechanical history of the various surfaces involved. Therefore, it is preferred to determine the-precise conditions requisite to optimum selective pharging. As hereinbefore set forth, when the silica fraction containingcationic reagent is heated and cooled, it has been observed that the particles are, to some extent, differentially charged. However, the particles may be charged'by contact electrification methods. Under certain conditions the surfaces of the mineral species are such that it is possible to electrify by mineral-metal contact electrification. [For example, if such contact causes high electrification with one mineral species and very low electrification with a second mineral species, a selective separation is possible. -By way of specific example, quartz-metal contact electrification will result in a relatively high surface charge density on the quartz compared to the corresponding surface charge density on Florida phosphate after phosphate metal contact electrification. However, even with these materials it is more desirable to employ quartz-phosphate contact electrification since this charging mechanism results in a surface charge density of opposite polarity on the two mineral species to be separated. A more complete discussion of charging mechanisms may be found in Fraas et al., Industrial and Engineering Chemistry, vol. 32, pp. 601- 602 (11940).

Ithas been discovered that charging of the particles may be accomplished by essentially particle-to-particle contact while the dry comminuted material is maintained at a temperature of at least 150 F. Ideally, the particles would not contact a metal or grounded metal surface during the charging operation, since as previously indicated, contact with grounded metal surfaces usually causes all particles to accept a negative charge. On the other hand, where the charging of the particles is accomplished esesntially by particle-to-par-ticle contact while at a temperature of at least 150 F., the surface charge density found on the mineral species in the ore is equal and opposite in sign. Accordingly, the charged particles move in opposite directions in an electrostatic field. Thus, in the process of the invention it becomes possible [to effectively separate non-conductive particles. The sign of the surface charge density to be expected in particle-to-par-ticle contact electrification, depends on the probability of the particle making contact with surface A, B, C, etc. and the relation of the surface energies that control the sign of contact electrification of the particles against A, B, C, etc. For example, if quartz contacts Florida phosphate rock at about 150 F, the resulting surface charge density on the quartz will be negative while that on the phosphate rock will be equally positive. If quartz is allowed to contact silica gel, the quartz will become charged positively and the silica gel equally negatively. Accordingly, the charge to be expected on quartz in a mixture of phosphate rock and silica gel depends on the probability of contacting silicia gel.

The desired particle-to-particle charging may be effected in a number of ways, such as by tumbling the particles down an elongated chute in such quantity that contact between the particles and the chute is at a minimum, Alternatively, the comminuted mineral, while maintainedat the proper temperature, may be delivered from the drying apparatus to the electrostatic separator by means of a, vibrating trough. At high throughput, the great preponderance of charging is engenedered by particle-to-particle contact rather than by contact of the particles with the trough. Suitable charging also may be obtained by air agitation of the hot, comminuted mineral.

' .The beneficiation of the mineral feed and the separation of theheavy mineral components is effected by passing the comminuted mineral as freely falling bodies through an external electrostatic field. It is essential to the satisfactory operation of the process that the particulate mineral, when delivered to and dropped into the electrostatic field, be dry and hot in order to achieve commercial1y acceptable beneficiation. It is further essential that the charge on the mineral be materially'unaltered as it is delivered to and passes through the external electrostatic field. Any corona discharge causing bombard- ;ment of the feed with ions or electrons or any, contact which materially will effect alteration of the charge on the individual particle as it is introduced into or passes through the external electrostatic field, must essentially be avoided. Otherwise, selectivity of charge on the respective particles resulting from the combination of steps preceding exposure to the external electric field will be deleteriously afiected and the degree of beneficiation of the material will be correspondingly reduced.

In practicing the process of the invention, therefore, it is necessary to employ an apparatus which minimizes the possibility of altering the previously acquired charge with corona discharge or of charging by inductive conduction such as is employed in the roll type conductive electrostatic separators such as the Johnson, Sutton and Carpco machines. It is desirable to employ either flat plates or relatively large rolls or cylinders as electrodes, which are specifically designed to minimize corona and to avoid metal contact in the presence of the external electrical field which results in inductive conduction and/ or alteration of the charge on the particles.

The surfaces of the oppositely charged electrodes of the electrostatic separator desirably will be positioned or formed at an angle to the normal path of flow of the material if undiverted by the electrostatic forces. Such arrangement of electrodes is provided to make the angle of divergency as great as possible, thus permitting the separation of materials with dividers to be more readily accomplished. Although a variety of electrostatic apparatus may be employed in the process of the invention, it is preferred that the electrostatic field be created by oneor' more pairs of spaced, oppositely charged electrodes, the lower portions of which curve outwardly from the perpendicular; The paired electrodes are desirably secured in place by members with smooth, convex surfaces. Although the field gradient may vary considerably, ithas been found that a field gradient of from about 6,000 to about 15,000 volts per inch is suflicient for most separations. In the electrostatic separation the silica particles are substantially separated from the heavy minerals and phosphate values. "Following this procedure it has been possible to produce a concentrate consisting of only 30% to 40% of the initial feed weight which contains of ihedphosphate 'and 98% of the heavy minerals in the The concentrate obtained from the electrostatic separation step contains the major portion of the phosphate and the heavy minerals. It has now been found that substantial separation of the heavy minerals from the phosphate in this concentrate may be effected when the concentrate is differentially charged as described and is then subjected to another electrostatic separation operation. This second electrostatic separation is elfected in substantially the manner set forth above; however, the operating conditions need not necessarily be the same as used in the first electrostatic separation step. Since in the first electrostatic separation the heavy minerals and the phosphate appeared in the same concentrate and were substantially separated from the silica, while in the second electrostatic separation the heavy minerals are separated from the phosphate, this represents a reversal of the heavy mineral fraction. In other words, in the first electrostatic separation the heavy minerals had substantially the same charge as the phosphate and went with the phosphate while in the second electrostatic separation the charge on the heavy minerals is of a difierent nature than the charge on the phosphate which eflfects a separation of the heavy minerals from the phosphate. One theory of such a shift in separation is hereinbefore set forth. However, it is not intended that the present invention be limited to any particular theory since the exact mechanism is not definitely known.

It is preferable that the concentrate from the first electrostatic separation step be heated to an elevated temperature before subjecting it to the second electrostatic separation step. In general temperatures of between about 200 F. and about 1000 F. may be used and temperatures within the range of from about 650 F. to about 750 F. have produced good results.

The second electrostatic separation step eflfects a substantial separation of the heavy minerals from the phosphate values. A heavy minerals concentrate and a phosphate concentrate are, therefore, separately recovered. Each of these concentrates may be recovered as the final product or one or both of them may be further beneficiated if desired.

In order to give a fuller understanding of the invention, but with no intention to be limited thereto, the following specific examples are given:

EXAMPLE I A phosphate ore from the Florida pebble phosphate fields is subjected to a washing operation in order to remove slimes and other organic matter. The washed rock in an aqueous pulp is subjected to a screening or hydraulic sizing operation whereby the larger particles of rock are segregated from material which is approximately 35 mesh standard screen size. The --35 mesh material is then reagentized in an aqueous pulp containing about 70% solids with about one pound per ton of ore of a reagent comprising about 88% tall oil and about 12% kerosene. About 2 to 4 pounds of fuel oil is added and suflicient caustic soda is mixed into the mixture to give the latter a pH of about 8 to 9. The resultant pulp is then subjected to a flotation operation at a solids content of about 25% to 40% by weight in a Fagergren machine and a float product is recovered containing approximately 60% tricalcium phosphate, about 20% silica, and about 1% of metallic minerals.

This phosphatic float product is then treated with about five pounds per ton of solids of sulfuric acid (60 B.) in order to remove the reagents therefrom. The acidtreated product is washed until it is substantially neutral and is then reagentized in an aqueous pulp with a mixture of long-chain aliphatic amines, the latter comprising a mixture of about 73% of mono-octodecyl amine and about 24% monohexadecyl amine, together with small quantities of secondary and tertiary amines whose aliphatic groups contain between about 12 and 18 carbon atoms. This cationic reagent is preferably added in the form of acetic acid addition salt. The reagentized product is then subjected to a flotation operation at a solids content as previously described. The resultant froth product from this flotation contains a majority of the silica and about 2% to 6% by weight of metallic minerals. This siliceous float was heretofore usually sent to waste as a tailing and all of the heavy mineral values and phosphatic values therein were, therefore, lost.

A siliceous float product containing 20.05% BPL and 4.6% heavy minerals, prepared in the above described manner, and still containing the amine reagent, was dried and heated in a hot air oven at 700 F. for two hours. The material was removed from the oven and the particles cooled by agitation in air. When the particles cooled to approximately 300 F., the particles were dropped between electrodes at a rate of approximately 20.00 pounds per hour per foot of horizontal electrode width. The electrodes consisted of two spaced rows of 3" diameter aluminum tubes arranged with approximately 1" of space between the tubes. The rows of electrodes were approximately apart. The voltage impressed across the electrodes was approximately 70,000 volts.

Below the electrodes seven pans were arranged so as to collect seven separate fractions. The pans extended from one electrode to the other so as to collect all of the dropped material. 1200 grams of the material 'was dropped and after the dropping the material in eachjo'f the pans was weighed and analyzed. The-results of these weighings are given below in Table I. The pans were numbered consecutively from one electrode to the other.

Table I Percent BPL Percent Percent Wt, Wt., Assay Heavy Percent Heavy Heavy Pan gms. Percent Percent Min- Recd Min- Mm. BPL erals Cum. erals Rec'd Cum. vCum.

It may be seen from the above data that in pans '1, 2 and 3, 38.1% (30.1+6.6+2.0) by weight of the dropped material was collected. This 38.1% contained 90.87% of the BPL and 98.3% of the heavy minerals in the dropped materials. The heavy minerals concentration is considerably increased in the first three pans from the original 4.6%.

EXAMPLE II An electrostatic separation was effected on a siliceous float product substantially as indicated above in Example I. The results are tabulated below in Table II. The charged siliceous material contained 3.2% heavy minerals and 19.9% BPL.

Table II Percent BPL Percent Percent Wt., Wt., Assay Heavy Percent Heavy Heavy Pan gms. Percent Percent Min- Recd Min- Min.

BPL erals Ou n. erals Recid Cum. um.

EXAMPLE HI Another electrostatic separation was effected on a silica float product substantially as indicated above in Example I. The results are tabulated below in Table III. The charged siliceous material contained 4.2% heavy minerals and 14.83% BPL.

Table III Percent BPL Percent Percent Wt;., Wt., Assay Heavy Percent Heavy Heavy Pan gms. Percent Percent Min-' Recd Min- Min.

BPL erals Cum. erals Becfd Cum.- 011m.

The above Examples II and IIIillustrate the substantial separation of the phosphate values and heavy minerals from the siliceous material. It should be noted that in each of the three examples, the phosphate and heavy minerals remained in the sarne concentrate, "that is they were not substantially separated from each other.

EXAMPLE IV The material collected in pans 1 and 2 of Example 9 III were mixed together, reheated to 700 F., cooled to 300 F., difierentially charged and dropped to effect an electrostatic separation in the same manner as set forth above in Example I.

The material was collected ad analyzed as before. The results are given below in Table IV.

Table IV Percent Percent Heavy Heavy Assay Percent Minerals Minerals Pan Wt, Wt., Percent Heavy Cumula- Recd gms. percent BPL Minerals tive Stimula- This example illustrates that following the procedure of the present invention a high (70.25%) BPL product and a high (37.0%) heavy minerals fraction may be separately recovered.

The description of the invention utilized specific reference to certain process details; however, it is to be understood that such details are illustrative only and not by way of limitation. Other modifications and equivalents of the invention will be apparent to those skilled in the art from the foregoing description.

Having now fully described and illustrated the invention, what is desired to be secured and claimed by Letters Patent is set forth in the appended claims.

1. A method of concentrating the heavy minerals in a silica concentrate containing heavy minerals, silica and cationic flotation reagent, said silica concentrate having been obtained as a float product of a cationic flotation in a process for recovering phosphate values from a phosphate ore containing silica and heavy minerals which comprises heating said concentrate to a temperature within the range of from about 200 F. to about 1000 F., inducing the heated concentrate while still at a temperature of at least 150 F. to accept differential electrical charges, and passing the charged particles into an electrostatic field without substantial alteration of their charge to separate a heavy minerals concentrate.

2. A method of concentrating the heavy minerals in a silica concentrate containing heavy minerals, silica and cationic flotation reagent, said silica concentrate having been obtained as a float product of a cationic flotation in a process for recovering phosphate values from a phosphate ore containing silica and heavy minerals which comprises heating said concentrate to a temperature within the range of from about 200 F. to about 1000" F., cooling the heated concentrate to a temperature within the range of from about 150 F. to about 350 F., inducing the concentrate while still at a temperature above 160 F. to accept differential electrical charges, subjecting the charged particles while at a temperature above 150 F. to an electrostatic field without substantial alteration of their charge to separate a heavy minerals concentrate.

3. A method of concentrating the heavy minerals in a silica concentrate containing heavy minerals, silica and cationic flotation reagent, said silica concentrate having been obtained as a float product of a cationic flotation in a process for recovering phosphate values from a phosphate ore containing silica and heavy minerals which comprises heating said concentrate to a temperature within the range of from about 650 F. to about 750 F., cooling the heated concentrate to a temperature within the range of trout about F. to about 350 F., inducing the concentrate while still at a temperature above 150 F. to accept difierential electrical charges, subjecting the charged particles while at a temperature above 150 F. to an electrostatic field without substantial alteration of their charge to separate a heavy minerals concentrate. 4. A method of concentrating the heavy minerals in a silica concentrate containing heavy minerals, silica, phosphate values and cationic flotation reagent, said silica concentrate having been obtained as a float product of a cationic flotation in a process tor recovering phosphate values from a phosphate ore containing silica and heavy minerals which comprises heating said concentrate to a temperature within the range of from about 200 F. to about 1000 F., inducing the heated concentrate to accept difierential electrical charges, passing the charged particles into an electrostatic field without substantial alteration of their charge to separate a heavy minerals concentrate containing phosphate values, heating said heavy minerals concentrate to a temperature within the range of from about 200 F. to about 1000" F., subjecting the heated heavy minerals concentrate while still at a temperature above 150 F. to an electrostatic field without substantial alteration of the electrical charge and separately recovering a heavy minerals concentrate and a phosphate concentrate. 5. A method of concentrating the heavy minerals in a silica concentrate containing heavy minerals, silica, phosphate values and cationic flotation reagent, said silica concentrate having been obtained as a float product of a cationic flotation in a process for recovering phosphate values from a phosphate ore containing silica and heavy minerals which comprises heating said concentrate to a temperature within the range of trom about 650 F. to about 750 F., cooling the heated concentrate to a temperature within the range of from about 150 F. to about 350 F., inducing the concentrate while still at a temperature above 150 F. to accept diflerential electrical charges, passing the charged particles while at a temperature above 150 F. into an electrostatic field without substantial alteration of their charge to separate, and recovering a heavy minerals concentrate containing phosphate values, heating said heavy minerals concentrate to a temperature within the range of from about 650 F. to about 750 F., cooling the heated concentrate to a temperature within the range of from about 150 F. to about 350 F., inducing the material while at a temperature above 150 F. to accept differential charges, subjecting the difierentially charged material while still at a temperature above 150 F., to-an electrostatic field without substantial alteration of the electrical charge and separately recovering a heavy minerals concentrate and a phosphate concentrate.

References Cited in the file of this patent UNITED STATES PATENTS 2,593,43 1 Fraas Apr. 22, 1952 2,723,029 Lawver Nov. 8, 1955 2,744,625 Houston May 8, 1956 2,762,505 Lawver Sept. 11, 1956 2,805,769 Lawver Sept. 10, 1957 2,847,123 Lawver Aug. 12, 1958 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION August 9, 1960 Patent Noa 2 948 395 John H. Di smant certified that error appears in the-printed specification ered patent requiring correction and that the said Letters d as corrected below.

It is hereby of the above numb Patent should rea led this 11th day of Ap ad" read and line 58 for Signed and sea ril 1961.

(SEAL) Attest:

E T W. SWIDER ERN s ARTHUR w. CROCKER A ti Commissioner of Patents 

1. A METHOD OF CONCENTRATING THE HEAVY MINERALS IN A SILICA CONCENTRATE CONTAINING HEAVY MINERALS, SILICA AND CATIONIC FLOTATION REGENT, SAID SILICA CONCENTRATE HAVING BEEN OBTAINED AS A FLOAT PRODUCT OF A CATIONIC FLOTATION IN A PROCESS FOR RECOVERING PHOSPHATE VALVES FROM A PHOSPHATE ORE CONTAINING SILICA AND HEAVY MINERALS WHICH COMPRISES HEATING SAID CONCENTRATE TO A TEMPERATURE WITHIN THE RANGE OF FROM ABOUT 200*F. TO ABOUT 1000*F., INDUCING THE HEATED CONCENTRATE WHILE STILL A TEMPERATURE OF AT LEAST 150*F. TO ACCEPT DIFFERENTIAL ELECTRICAL CHARGES, AND PASSING THE CHARGED PARTICLES INTO AN ELECTROSTATIC FIELD WITHOUT SUBSTANTIAL ALTERATION OF THEIR CHARGE TO SEPERATE A HEAVY MINERALS CONCENTRATE. 